1. Field of the Invention
The present invention relates to a shutter device, and more particularly, to a shutter device with a multi-stage diaphragm.
2. Description of the Related Art
A conventional shutter device usually utilizes a motor or an electromagnetic valve to control a shutter and a diaphragm thereof. For example Taiwan Patent No. 1237158 discloses two electromagnetic valves. One of the electromagnetic valves control opening and closing of the shutter. The other controls switching a large diaphragm and a small diaphragm. Thus, the conventional shutter device has many elements. Meanwhile, if we use the electromagnetic valve to control the diaphragm, the diaphragm has only two stages for switching. If the diaphragm must be adjusted by multi-stages, additional electromagnetic valves are added. Referring to Taiwan Patent No. 200734807 and 200834808, a stepper motor is disclosed to control a multi-stage diaphragm. Only one electromagnetic valve is required to control opening and closing of the shutter. However, the conventional shutter devices still have a complex structure. Furthermore, the stepper motor is large and costly. Taiwan Patent No. 200734787 discloses a special hollow stepper motor to control a multi-stage diaphragm and a shutter. Thus, the structure is simplified, but the shutter device is also large and costly.